Stratified-charge internal combustion engines have been developed and tested for many years. The stratified-charge engine runs lean like a diesel engine at all times with an unthrottled air supply and with the air and fuel being mixed inside the chamber. Like the Otto cycle spark ignition gasoline engine, the stratified-charge engine has its combustion cycle or power stroke initiated by electrical igniters.
Diesel engines with compression-ignition have traditionally used high compression ratios to assure short ignition delays and quick ignition to address the problems of cold starting. The compression ratios have often been 16:1 for open chamber designs and 21:1 for divided chamber designs. The high compression ratios are accompanied with large peak firing pressures within the combustion chamber upon the compression-ignition of the fuel and air mixture. The large peak firing pressures require stouter and heavier engine structure to withstand the high firing pressures. The structural requirements add to the overall weight, bulk and cost of the engine. Furthermore, because of this requirement, gasoline and diesel engines did not have many components that were interchangeable. Neither engine could be economically and feasibly converted to the other type of engine.
A spark-ignition gasoline engine however has octane requirements. Many of the current engines can barely operate at a 10:1 compression ratio on 87 R+M/2 octane fuel. Many of these engines require a knock sensor intended to detect early detonation and automatically retard the spark timing if required.
Direct-injection stratified-charge (DISC) engines have always held out the promise of eliminating the restrictive octane requirements of spark ignition engines while eliminating the disadvantages of high combustion pressures found in diesel engines and providing smooth and quiet combustion by igniting the mixture with a spark and doing so with compression ratios and firing pressures at levels intermediate between those used in compression-ignition and spark-ignition engines. So far, results of practical applications have not been encouraging. Multi-fuel capability, theoretically possible with these concepts, has also been disappointing. A direct-injection stratified-charge engine can be much lighter compared to a diesel engine of similar displacement thereby increasing the effective power output per unit weight of engine.
Many attempts at direct-injection stratified-charge (DISC) engines have been made in the past with little commercial success. The performance results have always been disappointing particularly in the field of emission control. They were hampered, as proven by modern technology, by lack of air capacity due to their two OHV-pushrod designs and their hopelessly inadequate injection and ignition systems.
What is needed is a direct-injected stratified-charge engine that has improved energy and environmental performance under various conditions, achieved by solving the air capacity, injection constraints, ignition drawbacks, and combustion problems which afflicted the conventional engines.